Mobile and portable electronic systems, such as smartphones, tablet computers, multimedia devices, motor vehicles, and various other mobile and portable processor-based systems, utilize components that may respond or perform poorly, or even become dangerous, under excessive heating conditions. For example, lithium-based batteries, which are currently used in many types of mobile and portable electronic systems, can fail, ignite, or even explode when exposed to high temperatures (whether as a result of self-heating or a combination of self-heating and heating of other system components). Additionally, processors and other circuit components may fail or function inadequately when exposed to excessive temperatures.
Due to the undesirable results which can occur due to excessive heating within electronic systems, such systems typically include thermal management or protection circuits that monitor the temperatures within the systems and execute thermal mitigation procedures upon detecting undesirable temperatures. Thermal management circuits typically include one or more thermistors having resistances that change with temperature. The temperature-varying nature of a thermistor's resistance results in a temperature-varying output voltage, which can be converted by a processor into an estimated temperature based on the thermistor's voltage-to-temperature relationship. While the use of thermistors assists with thermal management, such components are reactive in nature, thereby resulting in a reactive thermal management system. The drawback to reactive thermal management schemes is that once an undesirable temperature is detected, aggressive thermal mitigation procedures rapidly take place. Such procedures may have undesired consequences, such as preventing receipt of incoming data or transmission of emergency information.
One external factor that causes electronic system heating is a rise in ambient temperature surrounding the electronic system. Ambient temperature may rise naturally, such as a result of solar heating, or mechanically, such as due to the use of other heat-generating devices or systems (e.g., other electronic systems or a heating, ventilation, and air conditioning (HVAC) system) proximate the electronic system. Solar heating is an especially important external heating factor where an electronic system or its environment is directly exposed to solar radiation. For example, where the electronic system is a portable electronic device that is directly exposed to solar radiation, the ambient temperature rise may include heating of the ambient air as well as heating of the electronic device's housing due to absorption of solar energy.
One example of an electronic system exposed to solar heating is illustrated in FIG. 1. In this example, an electronic system 101 (in this case, a smartphone) is positioned in a docking station 103 secured to a dashboard 105 of an automobile. The electronic system 101 is directly exposed to solar radiation (and therefore solar heating) through the automobile's windshield 107. Depending on the time of day, time of year, geographic location of the automobile, cloudiness of the sky, color of the dashboard 105 and/or the electronic system's housing, and other factors, the solar thermal load applied to the electronic system 101 may be sufficient, either alone or in combination with system operation-related heating, to activate thermal mitigation procedures within the electronic system 101. However, because such mitigation procedures are reactive and often aggressive once activated, they may result in undesirable, rapid degradations in performance of the electronic system.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated alone or relative to other elements or the elements may be shown in block diagram form to help improve the understanding of the various exemplary embodiments of the present invention.